Metallurgical process for the preparation of aluminum-boron alloys



United States Patent METALLURGICAL PROCESS FOR THE PREPARA- TION OF ALUMINUM-BORON ALLOYS Hugh S. Cooper, 16401 S. Woodland Road,

Shaker Heights, Ohio 44120 No Drawing. Filed Sept. 15, 1967, Ser. No. 668,192 Int. Cl. C22c 21/00 U.S. Cl. 75135 Claims ABSTRACT OF THE DISCLOSURE The preparation of an aluminum alloy containing boron as an essential alloying element in various amounts comprising mixing potassium fiuoborate with finely divided aluminum particles in which the latter is present in an amount sufficient to react with the potassium fiuoborate to release boron, compacting the mixture and heating the mixture to elevated temperature above the temperature for molten aluminum for reaction to release the boron and alloying the boron as it is released with molten aluminum to form the aluminumboron alloy.

This invention relates to an aluminum alloy containing boron as an essential alloying element and it relates more particularly to a method for the preparation of same.

Alloys of aluminum and boron are often employed as a master alloy which is added to aluminum for the purpose of introducing boron for its grain refining effects. Grain refinement of boron is amplified by the presence of titanium so that it is often desirable to formulate the master alloy of aluminum and boron also to contain titanium as an additional alloying element. The desired grain refinement effects are secured in the final aluminum alloy when the titanium is present in an amount within the range of 0.2% to 0.25% by weight and when boron is present in an amount 'within the range of 0.01% to 0.05% by weight.

To the present, considerable difficulty has been experienced in the preparation of a master alloy of aluminum and boron. One procedure has been to add potassium fiuoborate to molten aluminum with vigorous stirring. Still others have sought to add sodium borate or boric acid as the source for boron. Such processes have required the use of considerable amounts of expensive labor, the yield of boron is quite low, and it has been difficult to prepare alloys having a boron content in excess of 2.5% by weight. For the most part, the boron that is present in the alloy seems to be in the form of a reddish-brown sub-oxide believed to be B 0.

It is an object of this invention to provide a low cost and efiicient method for the preparation of an aluminum alloy containing almost any desirable amount of boron as an alloying element and it is a related object to produce an aluminum base alloy containing boron as an essential alloying element and in which the boron may be incorporated in amounts considerably greater than that heretofore capable of being achieved by the conventional methods for boron addition.

In accordance with the practice of this invention, potassium fiuoborate is provided in intimate mixture with the powdered aluminum for reaction therewith to reduce the boron containing salt to elemental boron in a reaction which is believed to correspond to the following:

The potassium fiuoborate and the aluminum powder are admixed with the aluminum powder preferably in Patented Mar. 31, 1970 an amount sufficient to react with potassium fiuoborate to release boron and more preferably in excess of the stoichiometric amount to insure reduction of all of the potassium fiuoborate and maximum recovery of boron although a lesser amount can be employed for conversion of less than all of the potassium fiuoborate. For example, when present in stoichiometric amounts, approximately 126 parts by weight of KBF will react with about 27 parts by weight of aluminum powder to yield 10.8 parts by weight of boron. When an excess of aluminum powder is employed, an alloy is produced in situ with the generated boron alloying with the aluminum formed of excess aluminum powder under reaction conditions.

The mixture of potassium fiuoborate and aluminum powder is compressed or otherwise compacted into suitable briquettes, rods or the like for reaction in the presence of molten aluminum, preferably accompanied with moderate stirring. While a protective atmosphere is not essential, it is preferred to carry out the reaction under a protective atmosphere, such as in an atmosphere of hydrogen or an inert gas such as helium or argon. When the mixture is formulated to contain aluminum powder in excess of that required to react with potassium fiuoborate, the reaction in the presence of molten aluminum is not essential since the excess aluminum powder provides the aluminum with which the boron formed in situ is alloyed to produce a high boron content aluminum alloy. The latter procedure is perhaps more expensive than the former by reason of the higher cost of aluminum powder by comparison with the aluminum ingot of which the molten aluminum bath is formed for insertion of the compact.

The aluminum powder is preferably employed in a particle size within the range of 10 to 200 mesh and preferably within the range of 20 to 40 mesh. The mixture of potassium fiuoborate and powdered aluminum is easily compacted under pressure into rods. briquettes or the like without the need for additional hinder or other materials that might contaminate the metal or alloys formed thereof or otherwise complicate the reaction. It is desirable uniformly to mix the powdered aluminum and potassium fiuoborate and to compact the mixture closely and intimately to associate the reactive components.

Having described the basic concepts of the invention, the illustration will be made by way of a few typical examples which are given by way of illustration, but not by way of limitation:

EXAMPLE 1 126 grams of potassium fiuoborate are uniformly mixed with 30 grams of powdered aluminum having a mesh size within the range of 20 to 40 mesh. The

mixture is pressed into briquettes and the briquettes are added to 200 grams of molten aluminum maintained at a temperature of 900 C. in a protective atmosphere of hydrogen. As the briquettes are added, the melt is slowly stirred and the reaction, which is mildly exothermic, is carried out to release nascent boron in situ in the molten aluminum bath for immediate alloying with the aluminum. A slag formed of KF and AIR, forms on the surface. After the slag has been removed and the metal cooled, an ingot is formed having a boron content of 3.6% by weight corresponding to a recovery of 70% of the boron.

EXAMPLE 2 252 grams of potassium fiuoborate and 130 grams of aluminum powder are uniformly mixed and pressed into rods. The amount of aluminum powder theoretically required to react with the potassium fluoborate is 54 gramsthe remainder is present to form aluminum for alloying with the boron as it is released. The rods are loaded into a graphite crucible and heated to a temperature of 1200 C. in an inert atmosphere of hydrogen, helium or argon. The ingot that is formed contains 19.7% by weight boron, corresponding to a recovery of about 90.7%. The alloy can be diluted with additional aluminum for the purpose of reducing the boron content to a more desirable value for use as a master alloy such as an aluminum alloy containing 3% boron.

The temperature for the reaction can be varied from the melting point temperature of aluminum or about 650 C. to a temperature somewhat above 1200 C. The higher temperatures are preferred because of the greater fluidity imparted to the slag to permit easier separation.

The ratio of molten aluminum or excess aluminum powder to potassium fluoborate can be varied over a fairly wide range, depending upon the boron content sought to be secured in the final alloy.

It will be apparent from the foregoing that I have provided a new and inexpensive process for the release of boron in situ in the presence of molten aluminum for immediate alloying whereby greater recovery of boron is achieved in a simple and efiicient manner to produce an aluminum-boron alloy of high purity and in which the amount of boron can be higher than that capable heretofore of being secured.

It will be understood that changes may be made in the details of the amounts of the reactive ingredients and reaction temperatures without departing from the spirit of the invention, especially as defined in the following claims.

Iclaim:

1. The method of producing an aluminum alloy in which boron is present as an essential alloying element comprising mixing potassium fluoborate and powdered aluminum, pressing the mixture into a compact and heating the compact to at least the temperature of molten aluminum whereby the reaction takes place to release boron, in accordance with the following equation:

and alloying the boron as it is released with aluminum to form the aluminum-boron alloy.

2. The method as claimed in claim 1 in which the powdered aluminum is present in an amount suflicient to react with the potassium fluoborate present in accordance with the equation of claim 1.

3..The method as claimed in claim 1 in which the compact is introduced into molten aluminum and the reaction takes place in the presence of the molten aluminum to release boron for immediate alloying with the molten aluminum.

4. The method as claimed in claim 3 in which the reaction is carried out in the presence of a protective atmosphere.

5. The method as claimed in claim 1 in which the aluminum powder is present in suflicient excess over and above the stoichiometric amount to provide the aluminum in which the released boron is alloyed.

6. The method as claimed in claim 5 in which the reaction is carried out in the presence of. a protective atmosphere.

7. The process for producing an aluminum alloy in which boron is present as an essential alloying element comprising mixing potassium fluoborate and powdered aluminum with the aluminum powder being present in an amount to release the boron from the potassium fluoborate, pressing the mixture into a compact, heating the compact to at least the temperature of molten aluminum for reaction to release boron from the potassium fluoborate, and alloying the released boron with aluminum to form the aluminum-boron alloy.

8. The process as claimed in claim 7 in which the aluminum powder is present in at least the ratio of 27 parts by weight of aluminum powder to 126 parts by weight of potassium fluoborate.

9. The process as claimed in claim 7 in which the powdered aluminum is present is substantial excess and in which the reaction is carried out at a temperature within the range of 900 to about 1200 C.

10. The process as claimed in claim 7 in which the reaction is carried out in the presence of an inert or protective atmosphere.

References Cited UNITED STATES PATENTS 1,921,998 8/1933 Bonsack -138 X 2,781,261 2/1957 Kamlet 75135 2,931,722 4/1960 Urban 75-138 FOREIGN PATENTS 801,916 9/1958 England. 587,266 11/1959 Canada. 612,045 1/1961 Canada.

L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 

